Settable compositions comprising remediated fly ash (rfa) and methods of cementing in subterranean formations

ABSTRACT

Some embodiments of the present invention comprise a method of cementing comprising: placing a settable composition into a well bore, the settable composition comprising RFA, hydraulic cement, and water; and allowing the settable composition to set. Other embodiments comprise a method of cementing comprising: placing a settable composition into a well bore, the settable composition comprising RFA, calcium hydroxide (lime), and water; and allowing the settable composition to set. Other embodiments comprise a settable composition comprising: RFA, hydraulic cement, calcium hydroxide, natural pozzolan and water; and allowing the composition to set. Other embodiments comprise a settable composition comprising RFA and any combination of hydraulic cement, calcium hydroxide, slag, fly ash, and natural or other pozzolan.

PRIORITY DATA

This patent application is a continuation application of allowed U.S.patent application Ser. No. 15/894,203, filed on Feb. 12, 2018, which isa non-provisional application of U.S. Provisional Patent App. No.62/463,079, filed on Feb. 24, 2017, each of which is hereby incorporatedby reference herein.

FIELD OF THE DISCLOSURE

The present invention relates to cementing operations and, moreparticularly to methods and compositions that comprise remediated flyash (RFA) with hydraulic cement, calcium hydroxide, Type S lime, naturalpozzolan, fly ash, silica fume, ground glass, slag, or a combinationthereof.

BACKGROUND OF THE DISCLOSURE

Molten lava, flash frozen upon explosive expulsion from the volcanicvent, instantly became what the Romans called “pozzolana”—pumicepozzolan, the key ingredient in Roman concrete. Roman structures such asaqueducts used volcanic ash as pozzolan in their concrete. Concretesusing natural (pumice) pozzolan have proven to last thousands of years.Pozzolans fortify concrete, providing protection by mitigating variousforms of chemical attack such as alkali-silica reaction (ASR), sulfateinduced expansion, efflorescence, as well as rebar oxidation anddebondment caused by the ingress of chlorides. Pozzolans also densifyconcrete, reducing porosity and permeability, thereby reducing chemicalingress and increasing long-term compressive strength and durability.

Fly ash, also known as flue-ash, is one of the residues generated incoal combustion and comprises the fine particles that rise with the fluegases. In an industrial context, fly ash usually refers to ash producedduring combustion of coal. Fly ash is generally captured byelectrostatic precipitators or other particle filtration equipmentbefore the flue gases reach the chimneys of coal-fired power plants.Depending upon the source and makeup of the coal being burned, thecomponents of fly ash vary considerably, but all fly ash includessubstantial amounts of silica (silicon dioxide, SiO₂), alumina (aluminumoxide, Al₂O₃), iron oxide (Fe₂O₃), calcium oxide (CaO), and variousmetals.

In the past, fly ash was generally released into the atmosphere, butpollution control mandated in recent decades now requires that it becaptured prior to release. Fly ash, particularly Class F fly ash, can beused as a pozzolan to enhance hydraulic cement or hydraulic plaster. Flyash can be used as a replacement for some of the Portland cement contentof concrete. Fly ash has historically been available at much lower costthan natural pozzolans as it is a waste material of coal-fired powerplants with associated disposal costs.

Fly ash pozzolan, which is typically less expensive than a naturalpozzolan, is generally used when chemical attack, such as alkali-silicareaction (ASR), is not expected to be severe. Furthermore, fly ashpozzolan is preferred when concrete with a low water-to-cement ratio isdesirable. In general, fly ash generally creates less water demand thandoes a natural pozzolan. However, when chemical attack, such as ASR, isexpected to be severe, a natural pozzolan is generally more effective atthe same replacement rates used for fly ash.

Two classes of fly ash are defined by ASTM C618: Class F fly ash andClass C fly ash. The primary difference between these classes is theamount of calcium, silica, alumina, and iron content in the ash. Thechemical properties of the fly ash are largely influenced by thechemical content of the coal burned.

The burning of harder, older anthracite, bituminous and lignite coalstypically produces Class F fly ash. This fly ash is pozzolanic innature, and contains less than 20% lime (CaO). Possessing pozzolanicproperties, the glassy silica and alumina of Class F fly ash requires acementing agent, such as Portland cement, quicklime, or hydrated lime,with the presence of water in order to react and produce cementitiouscompounds. Calcium Hydroxide (Ca(OH)₂), the major byproduct of thehydraulic reaction between cement and water, is the key chemical withwhich pozzolan reacts to form additional Calcium Silicate Hydrate(C-S-H), the binder in all Portland cement-based concretes.

Fly ash produced from the burning of younger lignite or subbituminouscoal, Class C fly ash, in addition to having pozzolanic properties, alsohas some self-cementing properties. In the presence of water, Class Cfly ash will harden and gain strength over time. Class C fly ashgenerally contains more than 18% lime (CaO). Unlike Class F fly ash,self-cementing Class C fly ash does not require an activator.

For the coal power industry, concrete has been a convenient market forfly ash. For companies making or using concrete, fly ash has been alow-cost source of pozzolans. However, recently, a supply problem hasstarted to emerge. Namely, due to increasing environmental regulationsof power plants, the quantity and quality of fly ash has beendecreasing. There is a declining availability of fly ash, particularlyClass F fly ash, of suitable quality for use as a pozzolan in concrete.This situation is expected to worsen in the coming years.

In cementing methods, such as oil well construction and remedialcementing, as well as geothermal and water well construction, settablecompositions are commonly utilized. As used herein, the term “settablecomposition” refers to a composition that hydraulically sets orotherwise develops compressive strength. Settable compositions may beused in primary cementing operations whereby pipe strings, such ascasing and liners, are cemented in well bores. In performing primarycementing, a settable composition may be pumped into an annulus betweena subterranean formation and the pipe string disposed in thesubterranean formation. The settable composition should set in theannulus, thereby forming an annular sheath of hardened cement (e.g., agrout sheath) that should support and position the pipe string in thewell bore and bond the exterior surface of the pipe string to the wallsof the well bore. Settable compositions also may be used in remedialcementing methods, such as the placement of cement plugs, and in squeezecementing for sealing voids in a pipe string, cement sheath, gravelpack, formation, and the like.

There is a need in the art for improved settable compositions containingcement for oil-field applications and other cementing and concreteapplications, and methods of using these settable compositions.

SUMMARY

Some variations provide a settable composition for cementing, thesettable composition comprising (a) remediated fly ash (“RFA”), (b)cement and/or calcium hydroxide, and (c) optionally water, wherein theremediated fly ash contains fly ash and a natural or other pozzolan, andwherein the natural or other pozzolan is present in the remediated flyash in a concentration of about 1 wt % to about 99 wt %.

The natural or other pozzolan may be a pozzolanic volcanic ash. In someembodiments, the natural or other pozzolan is derived from pumice,perlite, ignimbrites, or any other volcanic material. In variousembodiments, the natural or other pozzolan is selected from the groupconsisting of pumice, pumicite, perlite, volcanic ash, metakaolin,diatomaceous earth, silica fume, precipitated silica, colloidal silica,ignimbrites, vitrified calcium alumino-silicates, ground waste glass,calcined shale, calcined clay, zeolites, and combinations thereof.

The remediated fly ash may be certified under ASTM C618, ASTM C1697,and/or AASHTO M295 as a Class C pozzolan or a Class F pozzolan. In someembodiments, the remediated fly ash includes Tephra® RFA. In certainsettable-composition embodiments, the remediated fly ash consistsessentially of Tephra® RFA.

The remediated fly ash may be characterized by a mean particle size ofabout 1 micron to about 400 microns. The remediated fly ash may bepresent in an amount of about 1% to about 80% by weight of cementitiouscomponents in the settable composition.

In some embodiments, the remediated fly ash further contains slag,preferably (but not limited to) ground-granulated blast-furnace slag.

In some embodiments, the settable composition has a density of about 8pounds per gallon to about 16 pounds per gallon.

When the settable composition comprises cement, the cement may bePortland cement, for example. When the settable composition comprisescalcium hydroxide, the calcium hydroxide may be present in the form ofType S lime that itself forms a part of the settable composition.

The settable composition may further comprise at least one additiveselected from the group consisting of fly ash, slag, natural pozzolan,crystalline silica, amorphous silica fume, fumed silica, sodiumhydroxide, calcium chloride, sodium chloride, glass fiber, polymerfiber, hydratable clay, biomass ash, crushed glass, elastomers, polymerresins, latexes, and combinations thereof.

The composition may further comprise at least one additive selected fromthe group consisting of a set retarding additive, astrength-retrogression additive, a set accelerator, a weighting agent,an aggregate, a lightweight additive, a gas-generating additive, amechanical property enhancing additive, a lost-circulation material, afiltration-control additive, a dispersant, a fluid loss controladditive, a defoaming agent, a foaming agent, an oil-swellable particle,a water-swellable particle, a thixotropic additive, a water reducingadditive, and combinations thereof.

When water is present in the settable composition, the water may bepresent in an amount of about 25% to about 200% by weight ofcementitious components, for example. The water may be derived from awater source selected from the group consisting of culinary water,freshwater, saltwater, brine, seawater, recycled water, and combinationsthereof. The settable composition may be provided without any water orwith a reduced water content, and then at a later time, the desiredamount of water may be added to the settable composition.

Some variations provide a structure (e.g., cement sheath) containing ahardened material derived from a settable composition comprising:

(a) remediated fly ash;

(b) one or more of: (i) cement, (ii) calcium hydroxide, or (iii) Type Slime; and

(c) water,

wherein the remediated fly ash contains fly ash and a natural or otherpozzolan, and wherein the natural or other pozzolan is present in theremediated fly ash in a concentration of about 1 wt % to about 99 wt %.

Other variations provide a method of cementing comprising placing asettable composition into a well bore and allowing the settablecomposition to set, wherein the settable composition comprises:

(a) remediated fly ash;

(b) one or more of: (i) cement, (ii) calcium hydroxide, or (iii) Type Slime; and

(c) water,

wherein the remediated fly ash contains fly ash and a natural or otherpozzolan.

In some embodiments, the remediated fly ash includes, or consistsessentially of, Tephra® RFA.

The remediated fly ash may be characterized by a mean particle size ofabout 1 micron to about 400 microns. The remediated fly ash may bepresent in an amount sufficient to increase compressive strength of thesettable composition, compared to an otherwise-equivalent settablecomposition without the remediated fly ash. In some embodiments, theremediated fly ash is present in an amount of about 1% to about 80% byweight of cementitious components in the settable composition.

When the settable composition comprises cement, the cement may bePortland cement or another type of cement.

In various methods, the settable composition further comprises at leastone additive selected from the group consisting of fly ash, slag,natural pozzolan, crystalline silica, amorphous silica fume, fumedsilica, sodium hydroxide, calcium chloride, sodium chloride, glassfiber, polymer fiber, hydratable clay, biomass ash, crushed glass,elastomers, polymer resins, latexes, and combinations thereof.

In these or other methods, the settable composition further comprises atleast one additive selected from the group consisting of a set retardingadditive, a strength-retrogression additive, a set accelerator, aweighting agent, an aggregate, a lightweight additive, a gas-generatingadditive, a mechanical property enhancing additive, a lost-circulationmaterial, a filtration-control additive, a dispersant, a fluid losscontrol additive, a defoaming agent, a foaming agent, an oil-swellableparticle, a water-swellable particle, a thixotropic additive, a waterreducing additive, and combinations thereof.

Water may be present in an amount of about 25% to about 200% by weightof cementitious components. The water may be derived from a water sourceselected from the group consisting of culinary water, freshwater,saltwater, brine, seawater, recycled water, and combinations thereof.

In some methods, the settable composition is allowed to set in the wellbore at a temperature of greater than 120° F. In some methods, thesettable composition is allowed to set in the well bore in an annulusbetween a subterranean formation and a conduit in the well bore. Incertain embodiments, the method includes squeezing the settablecomposition in an opening, the opening comprising at least one openingselected from the group consisting of an opening in a subterraneanformation, an opening in a gravel pack, an opening in a conduit, and amicro-annulus between a cement sheath and a conduit.

Other variations provide a method of cementing comprising placing asettable composition and allowing the settable composition to set,wherein the settable composition comprises (a) remediated fly ash, (b)hydraulic cement, and (c) water, wherein the remediated fly ash containsfly ash and a natural or other pozzolan.

The remediated fly ash is preferably present in an amount sufficient toincrease compressive strength of the settable composition, compared toan otherwise-equivalent settable composition without the remediated flyash. The remediated fly ash may be present in an amount of about 1% toabout 80% by weight of cementitious components in the settablecomposition, and the hydraulic cement may be present in an amount ofabout 1% to about 95% by weight of the cementitious components in thesettable composition. The remediated fly ash may be characterized by amean particle size of about 1 micron to about 400 microns.

In some methods, the settable composition further comprises a naturalpozzolan. The natural pozzolan may be characterized by a mean particlesize of about 0.5 microns to about 15 microns, for example.

In some methods, the settable composition further comprises calciumhydroxide and/or Type S lime.

The settable composition may be placed into a well bore, such as (butnot limited to) an oil-field well bore. For example, the settablecomposition may be allowed to set in the well bore in an annulus betweena subterranean formation and a conduit in the well bore.

DESCRIPTION OF SOME EMBODIMENTS

Certain embodiments of the present disclosure will now be furtherdescribed in more detail, in a manner that enables the claimed inventionto be understood so that a person of ordinary skill in this art can makeuse of the present disclosure.

Unless otherwise indicated, all numbers expressing reaction conditions,concentrations, yields, and so forth used in the specification andclaims are to be understood as being modified in all instances by theterm “about.” Accordingly, unless indicated to the contrary, thenumerical parameters set forth in the following specification andattached claims are approximations that may vary depending at least uponthe specific analytical technique. Any numerical value inherentlycontains certain errors necessarily resulting from the standarddeviation found in its respective testing measurements.

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” include plural referents unless the contextclearly indicates otherwise. Unless defined otherwise, all technical andscientific terms used herein have the same meaning as is commonlyunderstood by one of ordinary skill in the art to which this disclosurebelongs. If a definition set forth in this section is contrary to orotherwise inconsistent with a definition set forth in patents, publishedpatent applications, and other publications that are incorporated byreference, the definition set forth in this specification prevails overthe definition that is incorporated herein by reference.

The term “comprising,” which is synonymous with “including,”“containing,” or “characterized by” is inclusive or open-ended and doesnot exclude additional, unrecited elements or method steps. “Comprising”is a term of art used in claim language which means that the named claimelements are essential, but other claim elements may be added and stillform a construct within the scope of the claim.

As used herein, the phrase “consisting of” excludes any element, step,or ingredient not specified in the claim. When the phrase “consists of”(or variations thereof) appears in a clause of the body of a claim,rather than immediately following the preamble, it limits only theelement set forth in that clause; other elements are not excluded fromthe claim as a whole. As used herein, the phrase “consisting essentiallyof” limits the scope of a claim to the specified elements or methodsteps, plus those that do not materially affect the basis and novelcharacteristic(s) of the claimed subject matter.

With respect to the terms “comprising,” “consisting of,” and “consistingessentially of,” where one of these three terms is used herein, thepresently disclosed and claimed subject matter may include the use ofeither of the other two terms. Thus in some embodiments not otherwiseexplicitly recited, any instance of “comprising” may be replaced by“consisting of” or, alternatively, by “consisting essentially of.”

As used herein, “RFA” refers to remediated fly ash, such as (but notlimited to) Tephra® RFA marketed by CR Minerals Company, Pueblo, Colo.,U.S. See U.S. Pat. No. 9,561,983, issued Feb. 7, 2017 and U.S. Pat. No.9,611,174, issued Apr. 4, 2017, which are hereby incorporated byreference herein for their teachings of various embodiments of RFAapplicable to the present invention.

RFA includes a fly ash and a remediation agent. The fly ash may be anytype of fly ash, such as (but not limited to) waste fly ash, ASTM C618Class C fly ash, ASTM C618 Class F fly ash, or another type of fly ash.The remediation agent may be a natural pozzolan, another type ofpozzolan (other than fly ash), slag, silica fume, ground glass, ungroundexpanded shale, unground expanded clay, rice husk ash, or a combinationthereof.

The present invention relates to cementing operations and, moreparticularly, to compositions that comprise RFA with cement, calciumhydroxide, natural or other pozzolan, or a combination thereof, andmethods of using such compositions. There may be several potentialadvantages to the methods and compositions of the present disclosure,only some of which may be alluded to herein. One of the many potentialadvantages of some embodiments is that the inclusion of RFA in thesettable composition has been shown to increase the compressive strengthof the settable composition. Another potential advantage of someembodiments is that the RFA, cement, Type S lime, calcium hydroxide,natural or other pozzolan, or a combination thereof may be used toreduce the amount of a higher-cost component, such as hydraulic cement,resulting in a more economical settable composition. Yet anotherpotential advantage of some embodiments is that a reduction of theamount of cement in a settable composition will reduce the carbonfootprint of the cementing operation.

The present disclosure facilitates the removal of poor-quality fly ashfrom the waste stream or existing fly ash landfill/waste deposit andconverts it into a very useful product for which there is strong demandin the production of concrete for various infrastructure. The presentdisclosure is useful in oil field cementing slurries used to secure oilwell casings as well as prevent loss of oil to the formation duringextraction, among many other uses.

The present disclosure may be used by cement companies to produce a “1Pcement” per ASTM C595 and/or a performance cement per ASTM C1157. 1Pcements have been altered by the addition of a pozzolanic material toprovide pozzolanic advantages to the concrete in which it is mixed.Pozzolanic qualities include, but are not limited to: mitigating oneform of chemical attack or another, such as ASR, alkali-sulfatereactions, and the damaging effects of chloride ingress, particularlythe oxidation and debonding of reinforcing steel; concrete densificationand impermeability enhancement, increased long-term compressivestrength, and mitigation of efflorescence.

Embodiments of the settable composition may comprise RFA with cementand/or calcium hydroxide, Type S lime, slag, silica fume, ground glass,a natural or other pozzolan, or a combination thereof. Embodiments ofthe settable composition further may comprise water, for example, in anamount sufficient to form a pumpable slurry. In one particularembodiment, the settable composition may comprise a cementitiouscomponent that comprises RFA and hydraulic cement. In anotherembodiment, the settable composition may comprise a cementitiouscomponent that comprises RFA and calcium hydroxide (lime). In yetanother embodiment, the settable composition may comprise a cementitiouscomponent that comprises RFA, calcium hydroxide, and a natural pozzolan.In yet another embodiment, the settable composition may comprise acementitious component that comprises RFA, hydraulic cement, calciumhydroxide, and a natural pozzolan. Other optional additives may also beincluded in the settable compositions as desired, including, but notlimited to: fly ash, slag, phosphate cement, calcium sulfoaluminum (CSA)cement, Type S lime, ground glass, silica fume, or combinations thereof.Embodiments of the settable compositions may be foamed and/or extendedto reduce the density of the cementitious compound as needed or desiredby those of ordinary skill in the art.

The settable compositions of some embodiments preferably have a densitysuitable for a particular application as desired by those of ordinaryskill in the art, with the benefit of this disclosure. In someembodiments, the settable compositions may have a density in the rangeof from about 8 pounds per gallon (“ppg”) to about 16 ppg. In otherembodiments, the settable compositions may be foamed to a density in therange of from about 8 ppg to about 13 ppg.

Embodiments of the settable composition generally include RFA. RFA maybe a non-spec flue ash or non-spec fly ash or Class C fly ash that hasbeen remediated through a beneficiation process utilizing a naturalpozzolan or other pozzolan, slag, silica fume, ground glass, or acombination thereof as the remediation agent. Alternatively, oradditionally, other types of fly ash may be utilized. The RFA includesfly ash combined with a natural or other pozzolan. By “combined” it ismeant that the fly ash and natural or other pozzolan are physicallymixed or ground together; chemical reactions will typically not occurwithout the addition of water, although chemical combinations (such asequilibrium exchange reactions) are by no means excluded.

This patent application hereby incorporates by reference herein U.S.Pat. No. 9,561,983, issued Feb. 7, 2017 and U.S. Pat. No. 9,611,174,issued Apr. 4, 2017, as disclosing RFA that may be used, withoutlimitation, in the present invention.

A non-spec fly ash is waste material—usually derived from a coal-firedpower generation plant—that has been designated for ponding or landfilldue to the material's inability to meet industry standards related tochemical or physical specifications required for use in cement orconcrete. Beneficiation with a remediation agent can transform orupgrade the non-spec fly ash into a spec fly ash (RFA) that meets allthe standards of ASTM C1697, ASTM C618, and/or AASHTO M295 forcertification and use in cementitious systems and concrete. Theremediation agent may be a premium natural pozzolan, for example, toremediate a non-spec fly ash.

In some embodiments, the RFA is certified under ASTM C618 (“StandardSpecification for Coal Fly Ash and Raw or Calcined Natural Pozzolan forUse in Concrete”) or under ASTM C1697 (“Standard Specification forBlended Supplementary Cementitious Materials”) as a Class C or Class Fpozzolan. In these or other embodiments, the composition may becertified under AASHTO M295 (“Standard Specification for Coal Fly Ashand Raw or Calcined Natural Pozzolan for Use in Concrete”) as a Class Cor Class F pozzolan. Both ASTM C618 and AASHTO M295 are hereby entirelyincorporated by reference herein. It is also noted that RFA compositionsaccording to this disclosure may be alternatively, or additionally,certified under other standards or regulations, either presentlyexisting or developed in the future, in the U.S. or other countries.

RFA generally outperforms both originally certified fly ashes, as wellas raw natural pozzolans. In other words, the beneficiation of anon-spec ash or Class C fly ash with a natural pozzolan remediationagent, precisely blended, results in a superior supplementalcementitious material. This benefit affords the operator the ability tomix settable compositions at lower cost and increased performance.

It has been discovered (see the Examples herein) that the addition ofRFA with hydraulic cement or calcium hydroxide, or both hydraulic cementand calcium hydroxide, provides unexpected increases in compressivestrengths. In accordance with some embodiments, RFA may be used toincrease the compressive strength of settable compositions comprisingcement or calcium hydroxide. In addition, RFA may increase thecompressive strength of settable compositions comprising hydrauliccement, lime, natural pozzolans, or a combination thereof. Without beinglimited by speculation, it is believed that the RFA provided herein isparticularly suited for use at elevated well bore temperatures, such asat temperatures greater than about 80° F., greater than about 120° F.,or greater than about 140° F.

In one embodiment, RFA may be used, among other things, to replacehigher-cost cementitious components, such as Portland cement, resultingin more economical settable compositions. In addition, substitution ofthe Portland cement with the RFA should result in a settable compositionwith a reduced carbon footprint.

In some embodiments, RFA may be produced to any size suitable for use incementing operations. In some embodiments, the RFA is produced to a meanparticle size of about 1 micron to about 1000 microns, such as about, orat least about, or at most about 1, 10, 25, 50, 75, 100, 150, 200, 250,300, 400, 500, 600, 700, 800, or 900 microns. The mean particle sizecorresponds to D50 (mid-point) values as measured by commerciallyavailable particle size analyzers, such as those manufactured by MalvernInstruments, Worcestershire, United Kingdom. In some embodiments, theRFA is produced to a minimum particle size of about 0.1, 0.5, 1, 5, 10,or 25 microns. In these or other embodiments, the RFA is produced to amaximum particle size of about 10, 50, 100, 200, 500, or 1000 microns.

In some embodiments, within the RFA, a natural pozzolan is present in aconcentration of about 1 wt % to about 99 wt %, such as about 10 wt % toabout 90 wt %, about 30 wt % to about 70 wt %, about 40 wt % to about 60wt %, or about 60 wt % to about 70 wt % of the pozzolanic composition.In various embodiments, a natural pozzolan is present in the RFA in aconcentration of about 1, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55,60, 65, 70, 75, 80, 85, 90, or 95 wt % of the RFA composition. Invarious embodiments, fly ash is present in the RFA in a concentration ofabout 1, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75,80, 85, 90, or 95 wt % of the RFA composition.

In some embodiments of the RFA composition, a weight ratio of thenatural or other pozzolan to the fly ash is from about 0.01 to about100, such as about 0.1 to about 10, or about 1 to about 2. In variousembodiments, the weight ratio of the natural or other pozzolan to thefly ash is about 0.02, 0.05, 0.1, 0.2, 0.3, 0.5, 0.8, 1, 2, 3, 5, 8, 10,15, 25, 50, 75, or 90, for example.

In some embodiments, a natural or other pozzolan is selected from thegroup consisting of pumice, pumicite, perlite, tuff, rhyolite, tephra,volcanic ash, calcined shale, calcined clay, metakaolin, silica fume,ground glass, diatomaceous earth, fumed silica, precipitated silica,colloidal silica, ignimbrites, vitrified calcium aluminosilicates,zeolites, opalines, ground waste glass, finely ground sand, andcombinations or derivatives thereof. A preferred natural pozzolan may bea pozzolanic ash, such as (but not limited to) a pozzolan derived frompumice or perlite.

Pumice, and/or pumicite, a type of volcanic ash, is a volcanic rock thatconsists of highly vesicular rough textured volcanic glass, which may ormay not contain crystals. Pumice is created when super-heated, highlypressurized rock is violently ejected from a volcano. Pumice is composedof highly micro-vesicular pyroclastic glass with thin, translucentbubble walls of extrusive igneous rock. It is commonly, but notexclusively, derived of silicic or felsic to intermediate compositionmagma (e.g., rhyolitic, dacitic, andesite, pantellerite, phonolite, ortrachyte). Pumice is commonly pale in color, ranging from white, cream,blue or grey, to green-brown or black.

Perlite is an amorphous volcanic glass that has a relatively high watercontent, typically believed to be formed by the hydration of obsidian.Scoria is another vesicular volcanic rock that differs from pumice inhaving larger vesicles and thicker vesicle walls and being dark coloredand denser.

Silica fume is an amorphous, ultrafine powder that may be obtained fromsilicon-ferrosilicon alloy production. Silica fume may meetspecifications under ASTM C1240. Fumed silica may be obtained from flamepyrolysis of silicon tetrachloride or from quartz sand vaporized at hightemperature in an electric arc. Precipitated silica may be produced byprecipitation from a solution containing silicate salts. Colloidalsilica is a suspension of fine amorphous, nonporous, and typicallyspherical silica particles in a liquid phase.

Ignimbrite is a volcanic rock consisting essentially of pumicefragments, formed by the consolidation of material deposited bypyroclastic flows.

Diatomaceous earth is a naturally occurring, soft, siliceous sedimentaryrock that is readily converted into a fine powder.

Slag is a glass-like byproduct generated after a desired metal has beenseparated (i.e., smelted) from its raw ore. Slag is usually a mixture ofmetal oxides and silicon dioxide. Slags can contain metal sulfides andelemental metals. Ferrous and non-ferrous smelting processes producedifferent slags. The smelting of copper and lead in non-ferroussmelting, for instance, is designed to remove the iron and silica thatoften occurs with those ores, and separates them as iron-silicate-basedslags. Slag from steel mills in ferrous smelting, on the other hand, isdesigned to minimize iron loss and mainly contains oxides of calcium,silicon, magnesium, and aluminum.

In some embodiments, slag is specifically ground-granulatedblast-furnace slag. Ground-granulated blast-furnace slag may be obtainedby quenching molten iron slag (a by-product of iron and steel-making)from a blast furnace in water or steam, to produce a glassy, granularproduct that is then dried and ground into a fine powder. This type ofslag is also sometimes referred to as “slag cement.” In certainembodiments, the slag employed herein meets specifications as a slagcement per ASTM C989.

In some embodiments, vitrified calcium aluminosilicate pozzolans may bemade from recycled glass or fiberglass powders, from finely ground freshglass powders, or a combination thereof.

In some embodiments, the natural or other pozzolan contains amorphoussilica, amorphous alumina, and iron. The natural or other pozzolan ofsome embodiments is selected for its silica content. The natural orother pozzolan of some embodiments is selected for its alumina content.The natural or other pozzolan of some embodiments is selected for itscombined silica/alumina and iron content.

In some embodiments, the natural or other pozzolan is selected for itshigh silica content and pozzolanic strength to be used as an additive toremediate poor quality fly ash to a degree that will transform thepreviously unusable fly ash into a useful RFA.

In some embodiments, the natural or other pozzolan is selected for itsparticle-size distribution, surface area, particle-shape distribution,density, viscosity, or other properties. For example, pumice-derivedpozzolans may have an angular shape that sometimes creates higher waterdemand than fly ash pozzolans, which tend to have a spherical shape thatcreates less water demand.

In some embodiments, a natural or other pozzolan has a chemical contentcomprising a minimum of 85 wt % combined silica and alumina, and acalcium hydroxide content of less than 2 wt %.

Certain embodiments are predicated on fly ash remediating agents thatare not necessarily pozzolanic, or less pozzolanic than natural or otherpozzolans disclosed herein. In some embodiments, slag is employed as aremediating agent. Some embodiments thus provide a settable compositionfor cementing, the settable composition comprising (a) remediated flyash, (b) cement and/or calcium hydroxide, and (c) optionally water,wherein the remediated fly ash contains fly ash and slag, and whereinthe slag is present in the remediated fly ash in a concentration ofabout 1 wt % to about 99 wt %. Natural or other pozzolans mayadditionally be included, along with the slag.

In some embodiments, Type S lime is employed as a remediating agent.Some embodiments thus provide a settable composition for cementing, thesettable composition comprising (a) remediated fly ash, (b) cementand/or calcium hydroxide, and (c) optionally water, wherein theremediated fly ash contains fly ash and Type S lime, and wherein theType S lime is present in the remediated fly ash in a concentration ofabout 1 wt % to about 99 wt %. Natural or other pozzolans mayadditionally be included, along with the Type S lime.

The RFA composition may or may not include components in addition to thefly ash and the remediating agent. For example, additives or admixturesmay also be introduced. These additives may be added to adjust theproperties of the RFA composition itself, or to provide admixtureproperties for the ultimate cement or concrete. The RFA composition maycomprise an additive to adjust viscosity. The RFA composition mayfurther comprise an additive to adjust water demand of the compositionin concrete. Also, impurities may be present.

In some embodiments, the RFA is blended with hydraulic Portland cement,slag, calcium hydroxide (lime), and/or Type S lime. In some embodiments,the RFA/cement mixture contains hydraulic cement in an amount of about25% to about 75% by weight of the mixture and RFA in an amount of about25% to about 75% by weight of the mixture. In one embodiment, thehydraulic cement may be a Portland cement classified as ASTM Type I-Vcement or API spec Portland cements designated as Class A, Class B,Class C, Class G, or Class H. In accordance with embodiments, thehydraulic cement and RFA may be combined and produced to any sizesuitable for use in cementing operations. In other embodiments, thehydraulic cement and RFA may be sized prior to combination. In someembodiments, the RFA/cement mixture has a mean particle size of about0.1 microns to about 400 microns, or about 0.5 microns to about 50microns, such as 0.5 microns to about 10 microns. The mean particle sizecorresponds to D50 values as measured by commercially available particlesize analyzers such as those manufactured by Malvern Instruments,Worcestershire, United Kingdom.

The RFA may be included in the settable compositions in an amountsufficient to provide the desired compressive strength, density, costreduction, and/or reduced carbon footprint. In some embodiments, RFA maybe present in the settable compositions in an amount of from about 0.1%to about 99% by weight of cementitious components, preferably from about1% to about 80% by weight of cementitious components. Cementitiouscomponents include those components or combinations of components of thesettable compositions that hydraulically set, or otherwise harden, todevelop compressive strength, including, for example, RFA, calciumhydroxide, fly ash, natural pozzolan, slag, calcium sulfoaluminum,ground glass, silica fume, and the like.

The RFA may be present, in various embodiments, in an amount of about5%, about 10%, about 15%, about 20%, about 25%, about 30%, about 35%,about 40%, about 45%, about 50%, about 55%, about 60%, about 65%, about70%, about 75%, about 80%, about 85%, about 90%, or about 95% by weightof the cementitious components. In some embodiments, the RFA may bepresent in the settable composition in an amount from about 5% to about50% by weight of cementitious components. In other embodiments, the RFAmay be present in an amount from about 10% to about 50% by weight ofcementitious components. In yet other embodiments, the RFA may bepresent in an amount from about 20% to about 40% by weight ofcementitious components. One of ordinary skill in the art, with thebenefit of this disclosure, will recognize the appropriate amount of RFAto include for a chosen application, or can readily determine anappropriate amount of RFA by routine experimentation.

Embodiments of the settable compositions generally may comprise calciumhydroxide. The chemical analysis of calcium hydroxide (lime) varies frommanufacturer to manufacturer depending on a number of factors, includingthe particular kiln feed, or the exact chemistries of the limestonequarried from mines located near the production plants.

Some forms of calcium hydroxide (lime) contain a percentage ofnon-limestone materials, such as dolomite and siliceous rock. This typeof lime is commonly referred to as “Type S lime.” The pure form ofcalcium hydroxide is simply referred to as lime or calcium hydroxide.Type S lime is typically characterized by high early plasticity, highwater-retention values, limited oxide content, and minimal coarsefraction. In some embodiments, the Type S lime utilized herein meetsspecifications for Type S hydrated lime in ASTM C206 and/or ASTM C207.

The calcium hydroxide and/or Type S lime generally may exhibitcementitious properties, in that it may set and harden in the presenceof water and RFA, a natural pozzolan, or a combination thereof. Inaccordance with embodiments of the present invention, the calciumhydroxide may be used, among other things, to replace higher-costcementitious components, such as Portland cement, resulting in moreeconomical settable compositions. In addition, substitution of thePortland cement with the calcium hydroxide can result in a settablecomposition with a reduced carbon footprint.

The calcium hydroxide and/or Type S lime may be included in the settablecompositions in an amount sufficient to provide the desired compressivestrength, density, cost reduction, and/or reduced carbon footprint. Insome embodiments, the calcium hydroxide and/or Type S lime may bepresent in the settable compositions of the present invention in anamount from about 1% to about 95% by weight of cementitious components.The calcium hydroxide and/or Type S lime may be present, in certainembodiments, in an amount of about 5%, about 10%, about 15%, about 20%,about 25%, about 30%, about 35%, about 40%, about 45%, or about 50% byweight of cementitious components. One of ordinary skill in the art,with the benefit of this disclosure, will recognize the appropriateamount of calcium hydroxide and/or Type S lime (if any) to include for achosen application.

Embodiments of the settable compositions further may comprise a naturalpozzolan. The definition of a natural pozzolan is: “A raw or calcinednatural material (such as volcanic ash) which has pozzolanic properties”according to the American Concrete Institute (ACI). The definition of apozzolan is as follows: “A siliceous or silico-aluminous material thatwill, in finely divided form and in the presence of moisture, chemicallyreact with calcium hydroxide at ordinary temperatures to form compoundshaving cementitious properties (there are both natural and artificialpozzolans)” according to ACI.

Generally speaking, a natural pozzolan (NP) is a glassy(non-crystalline) siliceous rock consisting principally of amorphoussilica and amorphous alumina that exhibits cementitious properties inthe presence of hydrated lime (calcium hydroxide) and water. Naturalpozzolans include volcanic or volcanic-derived materials such as pumice,pumicite, tuff, ignimbrite, rhyolite, tephra, perlite, and volcanic ash.Natural pozzolans also include certain amorphous opalines, zeolites,diatomaceous earth (DE), calcined clays (such as metakaolin), andcalcined shales. Calcium hydroxide may be used in combination with thenatural pozzolan, for example, to provide sufficient calcium for thenatural pozzolan to set into a binder known as calcium silicate hydrate(CSH). This is the binder produced by Portland cements and water. It isalso produced when water, calcium hydroxide (lime), and pozzolans arecombined. In accordance with embodiments of the present invention, thenatural pozzolan may be used, among other things, to replace higher-costcementitious components, such as Portland cement, resulting in moreeconomical settable compositions. As previously indicated, replacementof the Portland cement should also result in a settable composition witha reduced carbon footprint.

Where present, the natural pozzolan may be included in an amountsufficient to provide the desired compressive strength, density, costreduction and/or reduced carbon footprint for a particular application.In some embodiments, the natural pozzolan may be present in the settablecomposition in an amount from about 1% to about 95% by weight ofcementitious components. For example, the natural pozzolan may bepresent in an amount of about 5%, about 10%, about 15%, about 20%, about25%, about 30%, about 35%, about 40%, about 45%, or about 50% by weightof cementitious components. In some embodiments, the natural pozzolanmay be present in the settable compositions in an amount in the range offrom about 5% to about 50% by weight of cementitious components. Inother embodiments, the natural pozzolan may be present in an amount fromabout 5% to about 40% by weight of cementitious components. In yet otherembodiments, the natural pozzolan may be present in an amount from about10% to about 30% by weight of cementitious components. Of the naturalpozzolan contained in the overall settable composition, any portion ofthe natural pozzolan (including from none to all) may be contained inthe remediated fly ash. One of ordinary skill in the art, with thebenefit of this disclosure, will recognize the appropriate amount of thenatural pozzolan to include for a chosen application.

The water that may be used in embodiments of the settable compositionmay include, for example, culinary water, freshwater, saltwater (e.g.,water containing one or more salts dissolved therein), brine (e.g.,saturated saltwater produced from subterranean formations), seawater,recycled water (e.g., water pumped out during drilling operations), orcombinations thereof. Generally, the water may be from any source,provided that the water does not contain an excess of compounds that mayundesirably affect other components in the settable composition. In someembodiments, the water may be included in an amount sufficient to form apumpable slurry. In some embodiments, the water may be included in thesettable composition in an amount in the range of about 40% to about200% by weight of cementitious components. In some embodiments, thewater may be included in an amount of about 40% to about 150% by weightof cementitious components. One of ordinary skill in the art, with thebenefit of this disclosure, will recognize the appropriate amount ofwater to include for a chosen application.

Embodiments of the settable compositions further may comprise lime. Incertain embodiments, the lime may be hydrated lime, such as (but notlimited to) Type S hydrated lime. The calcium hydroxide or Type S limemay be included in embodiments of the settable compositions, forexample, to form a hydraulic composition with other components of thesettable compositions, such as the RFA, natural pozzolans, fly ash,and/or slag. Where present, the calcium hydroxide or Type S lime may beincluded in the settable compositions in an amount sufficient for aparticular application. In some embodiments, the lime (e.g., as calciumhydroxide, Type S lime, or a combination thereof) may be present in anamount from about 1% to about 40% by weight of cementitious components.For example, the lime (e.g., as calcium hydroxide, Type S lime, or acombination thereof) may be present in an amount of about 5%, about 10%,about 15%, about 20%, about 25%, about 30%, or about 35% by weight ofcementitious components. One of ordinary skill in the art, with thebenefit of this disclosure, will recognize the appropriate amount of thelime (if any) and/or Type S lime to include for a chosen application.

It should be understood that use of Portland cement in embodiments ofthe settable compositions can be reduced or even eliminated to provide,for example, cost savings and/or reduced carbon footprint. Accordingly,embodiments of the settable compositions of the present invention maycomprise Portland cement in an amount of 0% to about 75% by weight ofcementitious components. For example, Portland cement may be present inan amount of about 1%, about 5%, about 10%, about 15%, about 20%, about25%, about 30%, about 35%, about 40%, about 45%, about 50%, about 55%,about 60%, about 65%, or about 70% by weight of cementitious components.In some embodiments, the Portland cement may be present in an amountfrom about 0% to about 20% by weight of cementitious components. Inother embodiments, the Portland cement may be present in an amount fromabout 0% to about 10% by weight of cementitious components. In yet otherembodiments, the settable compositions may be essentially free ofPortland cement, which means less than 1.0% by weight of cementitiouscomponents.

The Portland cements include those classified as Classes A, B, C, G, andH cements according to American Petroleum Institute, API Specificationfor Materials and Testing for Well Cements, API Specification 10, FifthEd., Jul. 1, 1990. In addition, the Portland cements include thoseclassified as ASTM C150 Type I, II, III, IV, or V.

One example of a suitable hydraulic cement comprises a mixture ofPortland cement and a natural pozzolan. In some embodiments, thecement/natural pozzolan mixture contains Portland cement in an amount ofabout 25% to about 75% by weight of the mixture and natural pozzolan inan amount of about 25% to about 75% by weight of the mixture. In someembodiments, the cement/natural pozzolan mixture contains about 40%Portland cement by weight and about 60% natural pozzolan by weight. Inaccordance with various embodiments, the Portland cement and naturalpozzolan may be combined and ground to any size suitable for use incementing operations. In other embodiments, the Portland cement andnatural pozzolan may be ground prior to combination. In someembodiments, the cement/natural pozzolan mixture of Portland cement andnatural pozzolan has a mean particle size of about 0.1 microns to about400 microns, such as about 0.5 microns to about 50 microns, or about 0.5microns to about 10 microns. The mean particle size corresponds to D50values as measured by commercially available particle size analyzerssuch as those manufactured by Malvern Instruments, Worcestershire,United Kingdom.

It is believed that hydraulic cement interground or blended with naturalpozzolan, when used in a settable composition in combination with RFA,may provide synergistic effects. For example, it is believed that thecombination of RFA and the cement/natural pozzolan mixture may providesignificantly higher compressive strength, particularly at elevated wellbore temperatures. Accordingly, the combination of RFA and thecement/natural pozzolan mixture may be particularly suited for use insettable compositions at elevated well bore temperatures, such as attemperatures greater than about 80° F., greater than about 120° F., orgreater than about 140° F.

Embodiments of the settable compositions further may comprise fly ash asan additional component, distinct from the RFA. A variety of fly ashesmay be suitable, including fly ash classified as Class C or Class F flyash according to American Petroleum Institute, API Specification forMaterials and Testing for Well Cements, API Specification 10, Fifth Ed.,Jul. 1, 1990. Note that this API Specification refers to ASTM C618 forclassification of fly ash types Class C and Class F. Natural pozzolans,Type N, are also included in ASTM C618. Class C fly ash comprises bothsilica and lime so that, when mixed with water, it may set to form ahardened mass. Class F fly ash generally does not contain sufficientlime, so an additional source of calcium ions is typically required forthe Class F fly ash to form a hydraulic composition. In someembodiments, lime may be mixed with Class F fly ash in an amount in therange of about 0.1% to about 25% by weight of the fly ash. Typically,the lime is hydrated lime, i.e. calcium hydroxide.

Where present, fly ash generally may be included in the settablecompositions in an amount sufficient to provide the desired compressivestrength, density, and/or cost. In some embodiments, when present, flyash may be present in the settable compositions in an amount of about 1%to about 99% by weight of cementitious components. In some embodiments,the fly ash may be present in an amount in the range of about 10% toabout 60% by weight of cementitious components. One of ordinary skill inthe art, with the benefit of this disclosure, will recognize theappropriate amount of the fly ash (if any) to include for a chosenapplication.

Embodiments of the settable compositions further may comprise slag. Slaggenerally does not contain sufficient basic or alkali material, so theslag (or the settable composition in general) further may comprise abase to produce a hydraulic composition that may react with water to setto form a hardened mass. Examples of suitable sources of bases include,but are not limited to, sodium hydroxide, sodium bicarbonate, sodiumcarbonate, calcium hydroxide, and combinations thereof. Slag may meetspecifications of ASTM C989, in some embodiments.

Where present, the slag generally may be included in the settablecompositions in an amount sufficient to provide the desired compressivestrength, density, and/or cost. In some embodiments, the slag may bepresent in the settable compositions in an amount of about 1% to about75% by weight of cementitious components. In some embodiments, the slagmay be present in an amount in the range of about 5% to about 50% byweight of cementitious components. One of ordinary skill in the art,with the benefit of this disclosure, will recognize the appropriateamount of the slag (if any) to include for a chosen application.

Embodiments of the settable compositions further may comprise a calcinednatural pozzolan such as metakaolin. Generally, metakaolin is a calcinednatural pozzolan that may be prepared by heating kaolin clay, forexample, to temperatures in the range of about 600° C. to about 800° C.In some embodiments, the metakaolin may be present in the settablecompositions in an amount of about 1% to about 75% by weight ofcementitious components. In some embodiments, the metakaolin may bepresent in an amount of about 10% to about 50% by weight of cementitiouscomponents. One of ordinary skill in the art, with the benefit of thisdisclosure, will recognize the appropriate amount of the metakaolin (ifany) to include for a chosen application.

Embodiments of the settable compositions further may comprise a calcinednatural pozzolan such as calcined shale. Among other things, calcinedshale, when included in the settable compositions, may react with excesslime to form a suitable cementing material, for example, calciumsilicate hydrate. A variety of shales may be suitable, including thosecomprising silicon, aluminum, calcium, and/or magnesium. A suitableshale comprises a vitrified (calcined) and finely divided shale.

Where present, the calcined shale may be included in the settablecompositions in an amount sufficient to provide the desired compressivestrength, density, and/or cost. In some embodiments, the shale may bepresent in the settable compositions in an amount of about 1% to about75% by weight of cementitious components. In some embodiments, the shalemay be present in an amount in the range of about 10% to about 35% byweight of cementitious components. One of ordinary skill in the art,with the benefit of this disclosure, will recognize the appropriateamount of the shale (if any) to include for a chosen application.

Embodiments of the settable compositions further may comprise pozzolaniczeolites. Zeolites generally are porous aluminosilicate minerals thatmay be either a natural or synthetic material. Synthetic zeolites arebased on the same type of structural cell as natural zeolites, and maycomprise aluminosilicate hydrates. As used herein, the term “zeolite”refers to all natural and synthetic forms of zeolite. Examples ofsuitable zeolites are described in more detail in U.S. Pat. No.7,445,669, which is hereby incorporated by reference. An example of asuitable source of zeolitic pozzolan is available from Bear RiverZeolite, Preston, Id., U.S. In some embodiments, the zeolite may bepresent in the settable compositions in an amount in the range of about1% to about 65% by weight of cementitious components. In certainembodiments, the zeolite may be present in an amount of about 10% toabout 40% by weight of cementitious components. One of ordinary skill inthe art, with the benefit of this disclosure, will recognize theappropriate amount of the zeolite (if any) to include for a chosenapplication.

Embodiments of the settable compositions further may comprise a setretarding additive. As used herein, the term “set retarding additive”refers to an additive that retards the setting of the settablecompositions of the present invention. Examples of suitable setretarding additives include, but are not limited to, ammonium, alkalimetals, alkaline earth metals, metal salts of sulfoalkylated lignins,organic acids (e.g., hydroxycarboxy acids), copolymers that compriseacrylic acid or maleic acid, or combinations thereof. Generally, whereused, the set retarding additive may be included in the settablecompositions in an amount sufficient to provide the desired setretardation. In some embodiments, the set retarding additive may bepresent in the settable compositions an amount of about 0.1% to about 5%by weight of cementitious components. One of ordinary skill in the art,with the benefit of this disclosure, will recognize the appropriateamount of the set retarding additive to include for a chosenapplication.

Optionally, other additional additives may be added to the settablecompositions of the present invention as deemed appropriate by oneskilled in the art, with the benefit of this disclosure. Examples ofsuch additives include, but are not limited to, strength-retrogressionadditives, set accelerators, weighting agents, fine and coarseaggregates, lightweight additives, gas-generating additives, mechanicalproperty enhancing additives, lost-circulation materials,filtration-control additives, dispersants, fluid loss control additives,defoaming agents, foaming agents, oil-swellable particles,water-swellable particles, thixotropic additives, water reducers, orcombinations thereof. Specific examples of these, and other, additivesinclude crystalline silica, amorphous silica fume, fumed silica, salts,fibers (e.g., cellulose fiber), hydratable clays, microspheres, ricehusk ash, elastomers, elastomeric particles, resins, latex, combinationsthereof, and the like. A person having ordinary skill in the art, withthe benefit of this disclosure, will readily be able to determine thetype and amount of additives useful for a particular application anddesired result.

As will be appreciated by those of ordinary skill in the art,embodiments of the settable compositions may be used in a variety ofsubterranean applications, including primary and remedial cementing.Embodiments of the settable compositions may be introduced into asubterranean formation and allowed to set therein. For example, thesettable composition may be placed into a space between a subterraneanformation and a conduit located in the subterranean formation.Embodiments of the cement compositions may comprise, for example, waterand one or more of RFA, hydraulic cement, calcium hydroxide, and naturalpozzolan.

In primary cementing embodiments, for example, a settable compositionmay be introduced into a space between a subterranean formation and aconduit (e.g., pipe strings or liners) located in the subterraneanformation. The settable composition may be allowed to set to form anannular sheath of hardened cement paste in the space between thesubterranean formation and the conduit. Among other things, the settablecomposition may form a barrier, preventing the migration of fluids inthe well bore. The settable composition also may, for example, supportthe conduit in the well bore.

In remedial cementing embodiments, a settable composition may be used,for example, in squeeze-cementing operations or in the placement ofcement plugs. By way of example, the settable composition may be placedin a well bore to plug a void or crack in the formation, in a gravelpack, in the conduit, in the cement sheath, and/or a micro-annulusbetween the cement sheath and the conduit.

In some variations, a concrete product or structure is provided,comprising the cementitious mixture as disclosed, or a reaction productthereof. In some variations, a concrete product or structure isprovided, comprising a pozzolanic composition or a reaction productthereof, wherein the pozzolanic composition comprises fly ash combinedwith a natural pozzolan. The concrete products or structures are notparticularly limited.

Some variations provide a structure (e.g., cement sheath) containing ahardened material derived from a settable composition comprising:

(a) remediated fly ash;

(b) one or more of: (i) cement, (ii) calcium hydroxide, or (iii) Type Slime; and

(c) water,

wherein the remediated fly ash contains fly ash and a natural or otherpozzolan, and wherein the natural or other pozzolan is present in theremediated fly ash in a concentration of about 1 wt % to about 99 wt %.

Other variations provide a method of cementing comprising placing asettable composition into a well bore and allowing the settablecomposition to set, wherein the settable composition comprises:

(a) remediated fly ash;

(b) one or more of: (i) cement, (ii) calcium hydroxide, or (iii) Type Slime; and

(c) water,

wherein the remediated fly ash contains fly ash and a natural or otherpozzolan.

Other variations provide a method of cementing comprising placing asettable composition and allowing the settable composition to set,wherein the settable composition comprises (a) remediated fly ash, (b)hydraulic cement, and (c) water, wherein the remediated fly ash containsfly ash and a natural or other pozzolan.

EXAMPLES

Tephra® RFA (CR Minerals Company, Pueblo, Colo., U.S.) is a patented,remediated fly ash that is a high-performance, high-surface-areapozzolan that meets or exceeds all criteria for ASTM C618 Class F flyash. The Tephra® RFA has a bulk density of 45 lb/ft³, with at least 90%of the particles passing a 325-mesh screen.

FIGS. 1 to 4 present experimental data for the use of RFA in mix designswhen replacing fly ash with RFA, or adding RFA to fly ash, in cementslurries relevant to oil field applications. FIG. 1 (experiments 1-6) isa control mix design with no RFA. FIG. 2 (experiments 7-10) is acement-based mix design employing RFA at various concentrations (20-40wt % on a dry basis). FIG. 3 (experiments 11-14) is a cement/lime-basedmix design employing RFA at various concentrations (28.5-57 wt % on adry basis). FIG. 4 (experiments 15-18) is a lime-based mix designemploying RFA at various concentrations (37-74 wt % on a dry basis).

In all experiments 1-18, a water/solids weight ratio of 0.5 was usedwithout any water reducers or other admixtures. The concentrations inthese tables are based on all components present except water (i.e., drybasis). The natural pozzolan is pumicite, in all cases when present.

The mix design itself is a slurry (grout) design which allowed for theuse of 2″×4″ cylinders to produce the samples. This simplified thebatching and curing process in terms of time and available space. Also,no aggregate is included the mix design. These samples rely on thehydraulic and pozzolanic reactions and subsequent relative strengthsbetween the various cementitious ingredients alone.

The 7-day and 28-day strength values are compressive strengths measuredafter curing for these time periods for which temperature was heldconstant at 73° F. The strength data shown is compressive strength inpounds/sq. inch (lbs/in² or psi). The 28-day compressive strength isimproved upon addition of RFA to the mix design.

These experiments demonstrate significant differences in oil fieldslurry performance between a standard Class F fly ash versus aremediated class F fly ash (RFA).

All publications, patents, and patent applications cited in thisspecification are incorporated herein by reference in their entirety asif each publication, patent, or patent application was specifically andindividually put forth herein, including (but not limited to) ASTM C618,AASHTO M295, ASTM C1697, API Spec 10A, and ISO Standard 10426-1.

In this detailed description, reference has been made to multipleembodiments of the disclosure and non-limiting examples relating to howthe disclosure can be understood and practiced. Other embodiments thatdo not provide all of the features and advantages set forth herein maybe utilized, without departing from the spirit and scope of the presentdisclosure. This disclosure incorporates routine experimentation andoptimization of the methods and systems described herein. Suchmodifications and variations are considered to be within the scope ofthe invention defined by the claims.

Where methods and steps described above indicate certain eventsoccurring in certain order, those of ordinary skill in the art willrecognize that the ordering of certain steps may be modified and thatsuch modifications are in accordance with the variations of thedisclosure. Additionally, certain of the steps may be performedconcurrently in a parallel process when possible, as well as performedsequentially.

Therefore, to the extent that there are variations of the disclosure,which are within the spirit of the disclosure or equivalents of theappended claims, it is the intent that this patent will cover thosevariations as well. The present disclosure shall only be limited by whatis claimed.

What is claimed is:
 1. A settable composition for cementing, the settable composition comprising (a) remediated fly ash, (b) cement and/or calcium hydroxide, and (c) optionally water, wherein said remediated fly ash contains fly ash and a natural pozzolan, wherein said natural pozzolan is present in said remediated fly ash in a concentration of about 1 wt % to about 99 wt %, and wherein said remediated fly ash is pozzolanic.
 2. The settable composition of claim 1, wherein said natural pozzolan is a pozzolanic ash.
 3. The settable composition of claim 1, wherein said natural pozzolan is derived from pumice, perlite, ignimbrites, or any other volcanic material.
 4. The settable composition of claim 1, wherein said natural pozzolan is selected from the group consisting of pumice, pumicite, perlite, volcanic ash, metakaolin, diatomaceous earth, silica fume, precipitated silica, colloidal silica, ignimbrites, vitrified calcium alumino-silicates, ground waste glass, calcined shale, calcined clay, zeolites, and combinations thereof.
 5. The settable composition of claim 1, wherein said remediated fly ash is characterized in that at least 90% of particles of said remediated fly ash pass a 325-mesh screen.
 6. The settable composition of claim 1, wherein said remediated fly ash is characterized by a bulk density of about 45 lb/ft³.
 7. The settable composition of claim 1, wherein said remediated fly ash is characterized by a mean particle size of about 1 micron to about 400 microns.
 8. The settable composition of claim 1, wherein said remediated fly ash is present in an amount of about 1% to about 80% by weight of cementitious components in said settable composition.
 9. The settable composition of claim 1, wherein said remediated fly ash further contains slag.
 10. The settable composition of claim 1, wherein said settable composition has a density of about 8 pounds per gallon to about 16 pounds per gallon.
 11. The settable composition of claim 1, wherein said settable composition comprises cement, and wherein said cement is Portland cement.
 12. The settable composition of claim 1, wherein said settable composition comprises calcium hydroxide.
 13. The settable composition of claim 12, wherein said settable composition comprises Type S lime that contains said calcium hydroxide.
 14. The settable composition of claim 1, wherein said settable composition further comprises at least one additive selected from the group consisting of slag, crystalline silica, amorphous silica fume, fumed silica, sodium hydroxide, calcium chloride, sodium chloride, glass fiber, polymer fiber, hydratable clay, biomass ash, crushed glass, elastomers, polymer resins, latexes, and combinations thereof, wherein said additive is different than said remediated fly ash.
 15. The settable composition of claim 1, wherein said settable composition further comprises at least one additive selected from the group consisting of a set retarding additive, a strength-retrogression additive, a set accelerator, a weighting agent, an aggregate, a lightweight additive, a gas-generating additive, a mechanical property enhancing additive, a lost-circulation material, a filtration-control additive, a dispersant, a fluid loss control additive, a defoaming agent, a foaming agent, an oil-swellable particle, a water-swellable particle, a thixotropic additive, a water reducing additive, and combinations thereof.
 16. The settable composition of claim 1, wherein said water is present.
 17. The settable composition of claim 16, wherein said water is present in an amount of about 25% to about 200% by weight of cementitious components.
 18. The settable composition of claim 16, wherein said water comprises at least one water source selected from the group consisting of culinary water, freshwater, saltwater, brine, seawater, recycled water, and combinations thereof.
 19. A structure containing a hardened material derived from a settable composition comprising: (a) remediated fly ash; (b) one or more of: (i) cement, (ii) calcium hydroxide, or (iii) Type S lime; and (c) water, wherein said remediated fly ash contains fly ash and a natural pozzolan, wherein said natural pozzolan is present in said remediated fly ash in a concentration of about 1 wt % to about 99 wt %, and wherein said remediated fly ash is pozzolanic. 